In trench storage dynamic random access memory (DRAM) devices, the capacitive elements of the devices are typically formed in deep trenches provided in the silicon substrate. As used herein, "deep" or "high aspect ratio" trenches are trenches having a depth that is typically 10 or more times the diameter of the trench. Although these DRAM devices function highly satisfactorily, as a result of the continuing effort to increase DRAM density and performance, a need exists to increase the period of time such devices retain a charge.
Retention time is adversely affected by charge leakage occurring via interstitial dislocations in portions of the silicon substrate adjacent the trench in which the capacitor is formed. Such dislocations are apparently caused, in part, by inherent compressive stresses in the trench fill material used in the fabrication of the capacitive device. The compressive stress in the fill causes the walls of the trench to bow outwardly, which deflection of the trench walls is believed to introduce dislocations in the substrate adjacent the walls of the trench.
Very high temperature anneal processes have been used to reduce the stress in oxide films. Unfortunately, such processes do not appear to have any appreciable affect on the stress in films of polycrystalline silicon ("poly-Si"). No other process are believed to be known for providing significant reduction in the stress in poly-Si films, particularly when used as the fill material for trench storage DRAMs.
Under certain conditions, voids will form in the fill of deep-trench capacitors during the formation thereof. One technique for minimizing the formation of such voids is disclosed in U.S. Pat. No. 4,977,104 to Sawada et al. This technique involves (a) depositing a first doped semiconductor film on a semiconductor substrate, (b) depositing a second undoped semiconductor film on the doped film, and (c) heat treating the substrate to cause the dopants to diffuse from the first film to the second film. In one example discussed in the Sawada et al. patent, a trench electrode having a phosphorous dopant concentration of 1.times.10.sup.20 /cm.sup.3 is formed using the method disclosed in this patent.
In the field of micro-mechanical devices, the need exists under certain circumstances to deform a given structure so that it assumes a predetermined configuration. For instance, silicon micro-mechanical cantilever structures of the type used in light deflector arrays and pressure sensors are known to bend in an undesirable manner due to intrinsic or thermal stresses in such structures. Under certain circumstances, such structures would have greater functionality and/or utility if such deformation could be controlled or eliminated.